Method of regulating vapor temperature



July 7, 1964 P. H. KOCH METHOD 0F REGULATING VAPOR TEMPERATURE 2 Sheets-Sheet 1 Filed Aug. 25, 1961 INVENToR Paul H. Koch ATTORNEY July 7, 1964 P. H. KOCH 3,139,869

METHOD 0E REGULATING VAPOR TEMPERATURE Filed Aug. 25, 1961 2 Sheets-Sheet 2 g-SSUMEETER HG2 ELVSM. TTQAES.

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United States Patent O 3,139,869 METHOD F REGULATING VAPOR TEMPERATURE Paul H. Koch, Akron, Ohio, assigner to The Babcock Wilcox Company, New York, N.Y., a corporation of New` Jersey Filed Aug. 25, 1961, Ser. No. 133,996 3 Claims. (Cl. 122-479) This invention relates ingeneral tofluid heating units and more particularly to a system for regulating temperature of superheat in a forced circulation once-through vapor generating and superheating unit. l

In a unit of the character described feed water 1s pumped intoone end of a continuous ow path, along which heat is supplied and from which sup-erheated vapor is discharged to a turbine or other point of usage. Generators of the forced flow type usually include through a part of the ilow path a number of serially connected passes in which the Working medium is raised in ternperature above the saturation temperature and each of which comprises a group of parallel flow circuits, with each circuit including a multiplicity of parallel long smallbore tubes. Other ow circuits may be provided for reheating the vapor and, in some cases, re-reheating the vapor. The working medium may be discharged from this continuous flow path at extremely high temperatures, for example, in the. order of 1050 F. Since, in operation, a uniform performance ofthe parallel circuits is desired, the circuits are disposed in relation to the gas flow path through the unit in amanner calculated tov give equal heat inputs to the circuits. However, perfection is difficult to attain and balanced heat input may be disturbed by unequal firingV of burners or by fouling of` the heat exchange surfaces to different degrees. There Will then be a tendency for the circuits to superheat vapors to different temperatures. Unequal superheated vapor temperaturesffrom theparallel flow circuits may also be occasioned' by maldistribution of the Working medium to the parallel flow circuits. This invention is directed to a systemfor regulating the temperatures of the vapor discharging from the parallel flow circuits to the end that such temperatures are uniform and constant over a wide load range.

The various featuresof novelty which characterize my invention are pointed out with particularity in the claims annexed to andforming a part of this specication. For a better understandingof the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in Whichl haveillustrated and described the preferred embodiment ofthe invention.

In the drawings:

FIG. l is a schematic illustration of a vapor generator of the forced flow once-through type.

FIG. 2 illustrates a schematic from a control system embodying my invention for the generator shown in FIG. 1, and

FIGS. 3 and 4 illustrate a modification which may be incorporated in the control system shown in FIG. 2.

As generators of the forced ilow type are Well known in the art, I have shown in FIG. 1 only the elements of such a generator in rudimentary form to assist in understanding my invention. However, the control system of the invention is particularly adapted for use in a forced flow once-through vapor generating and superheating unit designed for the production of superheated steam at pressures and temperatures above the critical pressure of 3206 p.s.i. and the critical temperature of 705 F., a unit of this general construction being described and claimed in a coJpending U.S. applicationof Paul H. Koch, Serial No. 685,119, filed September 20, 1957, now Patent No. 3,007,-

3,139,869 Patented July 7, 1964 ice 459. Also in FIG. 1 I have shown the points of measurement and regulationutilized in my control system which are referenced into the control diagrams of FIGS. 2 and 3.

Referring to FIG. 1 there is generally` indicated at 2 a vapor generator of the once-through forced flow type having a series iluid flow path including a vapor generating section 3, primary superheater 4 and a secondary superheater generally indicated at 5. As shown, the secondary superheater comprises a plurality of parallel flow circuits 6, 7, 8 and 9, each of which is constructed and arranged to separately discharge superheatedvapor directly to a turbine 16. Feed water from any suitable source is forced at high pressure. into the generator by means of a pump 11 driven by any suitable means, such as a motor or turbine, diagrammatically shown at 12. A controller 12A is provided for regulating the speed of the motor 12 and hence the rate at Which feed water is forced into and through the generator. Fuel and air for combustion are admitted to the. generator through conduits 13 and 14 respectively; and the gaseous products of combustion, after passing over the vapor generating and superheating surfaces, are discharged through an outlet, diagrammatically shown at 1S. Valves 13A `and 14A represent the customary regulating means forthe fuel and air respectively.

Disposed in the inlet to each secondary super-heater path or circuit is a spray attemperator, identified by the numbers 17, 18, 19 and 20. Such attemperators are Well known in the art and may take any conventionalform. Reference may be made, for example, to UnitedStates Patent 2,550,683to Fletcher et al. which illustrates and describes a suitable type. Water for the, attemperators is supplied through a conduit21` froml any suitable source. Frequently, but not always, the water for `the attemperators is obtained from the discharge of the pump 11. The ow of water toyeach attemperator may be regulated by suitable valves such as shown at 70, 71A, 71B and 71C.

In'FIG. 2 I show in diagrammatic form a control system for the generator shown in FIG. l. In accordance with my invention the control system of FIG. 2 is arranged to control the rate of firing in proportion to the load on the generator with readjustment as required to maintain a predetermined final steam temperature at the outlet at a selected one of the secondary superheater paths. Attemperating water isintroducediinto the inlet of this selected path at a scheduled rate sullicient to insure some attemperating Water being required in each of the other parallel flow secondary superheater paths to maintain the temperature at the outlet of each of these other paths at the same value as the iinal steam temperature of the outlet of the aforesaid selected path. Depending upon such conditions as the particular design of the generator under consideration, type of fuel burning equipment and the like, the scheduled rate at whichattemperating water is introduced into the selected path may remain constant over the entire range of generator operation, may increase with rating or, in some cases, even decrease with rating. In other words it may be said that in accordance with my invention the rate of tiring is adjusted to continually maintain a higher temperature than that desired at the outlets of the superheater paths and the temperature then reduced by attemperation to that desired. By initially adjusting tiring rate in accordance With load and having the ring rate readjustedfrom temperature, the effect of changes in load on iinal steam temperature is to a great extent minimized and anticipated to the end that relatively minor adjustments of ring rate from temperature are required.

IV have chosen to illustrate and describe my invention embodied in a pneumatically operated control system for the reason that such systems, as well as the components thereof, are well known and readily understandable by those familiar with the art. It will be apparent, however, as the description proceeds, that my invention could equally as well be embodied in a hydraulic or electrically operated system and the principles thereof utilized in manual control of the generator.

Referring now to FIGS. l and 2, I show at 22 a transmitter sensing the differential produced by a primary element 22A disposed in the feed pipe to the generator and generating a pneumatic loading pressure proportional to the rate of ow of feed water to the generator. Since the generator 2 is of the forced flow once-through type, the rate of flow of feed Water is equal to the rate of vapor generation or load or rating on the unit. The loading pressure generated by transmitter 22 is transmitted through a pipe 23 and by branch pipe 23A to the C chamber of a proportional relay 24 which may be, for example, of the type illustrated and described in U.S. Patent No. 2,805,678 to Michael Panich.

The relay shown at 24, as taught by Panich, may be used to obtain a variety of control actions such as proportional, proportional plus reset and proportional plus rate. A direct acting control may be obtained by introducing a loading pressure into the C or A chambers whereas an inverse action can be obtained by introducing a lloading pressure into the B chamber. By introducing loading pressures into both the A and B chambers and opening the C chamber to atmosphere a pressure at D proportional to the difference between the loading pressures introduced at A and B may be obtained, or a pressure at D may be obtained proportional to the sum of the pressures introduced into C and A. I therefore utilize the relay, such as shown at 24, to obtain various desired control actions which I will identify as the description proceeds.

The relay 24 serves to generate in output chamber D a control pressure proportional to the loading pressure introduced at C which is transmitted through a pipe 25 and Selector Station 26 to final control elements 13A and 14A controlling the supply of fuel and air respectively to the generator 2. The Selector Station 26 provides a means for transferring the control from Automatic to Remote Manual and may be of the type illustrated and described in U.S. Patent No. 2,747,595 to Paul S. Dickey.

While I have shown fuel and air controlled in parallel in accordance with generator load, as common in the art, sub-loop controls would normally be incorporated in the control system to maintain a predetermined fuel-air ratio, furnace draft and the like.

The control so far described operates to control firing in proportion to the load on the generator. By so doing approximately the correct temperature will be maintained at the outlet of the superheater paths 6, '7, S and 9. Howu e r ever, as previously stated, in accordance with my invention the ring is readjusted to maintain the desired outlet temperature in a selected one of the superheater paths. In the drawings I have shown a temperature transmitter 27 arranged to generate a loading pressure in accordance with the vapor temperature at the outlet of superheater path 6. This loading pressure is transmitted through a pipe 28 to a proportional plus reset relay 29. That is to say, the control pressure generated by the relay at output chamber D is a function both of the changes in loading pressure introduced into the relay and the time integral of the difference between the actual loading pressure and a predetermined or Set Point value of the loading pressure. As it is desired to have the rate of tiring vary inversely with changes in temperature, the loading pressure is introduced into the B chamber so that an increase in loading pressure, for example, causes a corresponding decrease in control pressure in D. The control pressure generated by relay 29 is transmitted through a pipe 30 to the A chamber of the relay 24 and hence changes therein produce proportionate changes in the output pressure of this last named relay.

Relay 29 being adjusted so that the Set Point corresponds to the desired outlet temperature, the control operates to vary the tiring rate in accordance with changes in load and to readjust the firing rate as required to maintain the desired outlet temperature. By virtue of the difference in time constants of the load responsive coritrol loop and the temperature responsive control loop, the control from temperature is inherently slow acting and serves to readjust the tiring rate after the initial and anticipating adjustment from load. As will be readily apparent the adjustments provided in relays 24 and 29 may be utilized to adjust the control in accordance with the system time constants or if necessary additional relays or control elements may be incorporated in the system for this purpose.

To insure that the tiring rate is maintained at a rate requiring some attemperation in superheater paths 7, 8 and 9 to maintain the desired temperature at the outlet of each of the paths, attemperating water is introduced into superheater path 6 at a rate corresponding to generator load. The loading pressure generated by transmitter 22 is transmitted through a branch pipe 23B to a proportional relay 31, the output pressure of which is transmitted through a pipe 32 to a proportional plus reset relay 33, the output pressure of which in turn is transmitted through a pipe 34, Selector Station 35 to attemperator valve 70. Also introduced into relay 33 is a loading pressure corresponding to the rate of flow of Water to the attemperator 17 as generated by a ow transmitter 36.

It may be said that the control system for attemperator 17 incorporates a constant ow control the Set Point of which is adjusted in accordance with generator load. That is to say, the control pressure generated by relay 31 is a function of load and this pressure introduced into the proportional plus reset relay 33 serves to establish the Set Point of this relay which is included in the constant ow control loop comprising valve 70 and tlow transmitter 36. Hence the control assures that a predetermined rate of ow of water to attemperator 17 will be maintained for each and every generator load. The control components may be provided with the necessary adjustments for establishing any desired relationship between generator load and attemperator water flow as will be apparent to those familiar with the art, the prime consideration being that the flow of attemperating water to attemperator 17 be maintained at the minimum required to assure some attemperation being required to maintain the desired outlet temperatures in superheater paths 7, S and 9. Ordinarily an increasing amount of attemperating water will be required with increasing load; however, with some generator designs a constant ow of attemperating water may be required over the entire range of operation of the generator or even a decreasing amount of attemperating Water with increasing generator load.

If due to malfunction of the control or for any other reason the temperature at the outlet of superheater path 6 should materially increase above the Set Point, the ilow of attemperating water should be increased above the scheduled value to avoid damage to the generator and associated equipment. To provide for this contingency incorporated in the control is a limit or over-riding control from the temperature at the outlet of superheater path 6. As shown the loading pressure generated by temperature transmitter 27 is transmitted by way of branch pipe 28A to a proportional plus reset relay 37, the output pressure of which is introduced into the C chamber of relay 31. The Set Point of relay 37 is adjusted to be materially above the Set Point normally maintained by the control from firing. For example, the control from tiring may be adjusted for a Set Point of 1050 F. and the over-riding control for a Set Point of 1060 F. Hence, normally the output pressure of relay 37 will remain at an extreme fixed value and have no effect on the normal control. However, should the temperature at the outlet of superheaterl path 6 increase above the predetermined limit the output pressure of relay 37 will correspondingly vary causing an increase inthe attemperating water as required Ato hold the temperature at or below the limit value.

The temperature control for each of the superheater paths 7, 8 and 9 is the same and I will therefore describe the control for superheater path 7 only. I have on the drawing indicatedcorresponding control elements for the control of the superheater paths 7, '3 and 9 by the same reference numbers Afollowed Vby reference letters A, yB and C respectively.

Temperature transmitterV 38A `generates a loading pressure corresponding to the temperature at the outlet of superheater path 7 which is transmitted by pipe 39A to a proportional plus reset relay 40A, thence to a proportional relay 41A, Selector Station 42A to attemperator valve 71A. The Set Point of relay 40A is adjusted so that the flow of the attemperating water is varied as required to maintain the desired outlet temperature.

Because of the relatively long time constants usually encountered it is sometimes desirable to superimpose upon the proportional plus reset control a rate action. As shown in FIG. 2, I may incorporate in the control a proportional plus rate relay 43A which serves to generate an output pressure corresponding both to the amount and rate of temperature change. This pressure is transmitted by way of pipe 44A to relay 41A so that it serves to modify the control pressure transmitted to valve 71A in accordance with the rate of change in the outlet temperature of superheater path 7.

It is sometimes desired to vary the temperature Set Point in accordance with generator load or to modify it from some factor such as, for example, exhaust hood temperature of a turbine supplied with vapor from the generator. I have shown in FIG. 2 the control arranged so that the Set Point of the temperature control is varied as a function of generator rating, it being apparent therefrom how modifying controls in general may be incorporated in the system if desired.

The loading pressure generated by ow transmitter 22 is transmitted to a proportional relay 45, then through pipe 46 to the B chambers of relays 37, 40A, 40B and 40C. The control pressure established by relay 45 varying with generator rating thus serves to correspondingly adjust the Set Points of the last named relays and hence the temperature maintained at the outlet of superheater paths 6, 7, 8 and 9.

I show the loading pressure generated by transmitter 22 introduced into the C and B chambers of relay 45 as illustrating the flexibility of the control to provide any desired functional relation between generator rating and the temperature Set Point. By adjustment of the proportional band of relay 45 the output pressure generated thereby may be made to increase with rating or decrease with rating. Manual Loader 47 and 3-way valve 48 are provided for transferring the temperature Set Point control from Automatic to Remote Manual. The 3-way valve is shown in the Automatic position. In the second position the loading pressure manually established in Loader 47 is transmitted to relays 37, 40A, 40B and 40C and provides a means for establishing a temperature Set Point independent of generator load.

In the arrangement shown in FIGS. l and 2, generator rating is adapted to load requirements by adjusting the rate of flow of feed water to maintain a desired outlet pressure. Therein pressure transmitter 50 generates a loading pressure corresponding to the pressure of the vapor in the turbine vapor supply distributor which is transmitted through a pipe 51 to a proportional plus reset relay 52 and thence by way of a pipe 53, Selector Station 54, and pipe 55 to motor control unit 12A.

In FIGS. 3 and 4 I show an alternate arrangement of ioad control wherein the pressure in the turbine supply line 49 is maintainedat desired value by means of a back pressure control valve 56. With this alternate arrange- .ment the loading pressure generated by transmitter 50 is transmitted from Selector Station 54 through a pipe 57 to the back pressure control valve 5,6. The Selector Station 54 maybe provided with a manually adjustable loader for manually establishing -a loading pressure transmitted .through a pipe 58 to the -B chamber of relay 52 to thereby provide a means for adjusting the Set VPoint of the control.

Further in accordance with the arrangement shown in FIGS. 3 and 4 feed water How Vis controlled to a constant value by having the loading pressure generated by transmitter 22 introduced .into a proportional plus reset relay 6i), the output lpressure of which is transmitted by way of a Selector Station-61 to motor control unit 12A. As shown, the Set Point of the constant iiow control is manually adjusted from Selector Station 61. It will be apparent however that if desired the Set Point may be adjusted automatically from any desired factor arranged to generate a proportionate loading pressure which is introduced into the A chamber of relay 60.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to` advantage without a corresponding use of other features.

What is claimed is:

l. The method of regulating vapor temperature in a fuel-fired forced flow vapor generator wherein the entering liquid is vaporized and then passed in parallel ow relation to a plurality of parallel ilow vapor superheating circuits, which comprises maintaining the temperatures of the vapor discharging from said superheater circuits at a substantially uniform and constant predetermined value over a wide range of loads by supplying attemperating liquid to one of said circuits in response to an increase in vapor temperature therein above said predetermined temperature value, and by varying the firing rate in response to deviations of the vapor temperature in another of said circuits from said predetermined temperature value in direction tending to increase the firing rate as the vapor temperature in said other circuit drops below said predetermined value and vice versa, while continuously supplying attemperating liquid to said other circuit throughout said predetermined load range in quantities sufficient to assure that said one circuit will always require some attemperating liquid to hold the vapor temperature therein at said predetermined temperature value.

2. The method of regulating vapor temperature in a fuel-red forced flow once-through vapor generator wherein the entering liquid is vaporized and then passed in parallel flow relation to a plurality of parallel flow vapor superheating circuits, which comprises maintaining the temperatures of the vapor discharging from said superheater circuits at a substantially uniform and constant predetermined value over a wide range of loads by varying the firing rate in response to deviations of the vapor temperature in one of said circuits from said predetermined value in direction tending to increase the firing rate as the Vapor temperature in said one circuit drops below said predetermined value and vice versa, while continuously supplying attemperating liquid to said one circuit throughout said predetermined load range, supplying attemperating liquid to each of the remaining circuits in response to an increase in vapor temperature therein above said predetermined temperature value, and maintaining the supply of attemperating liquid to said one circuit throughout said predetermined load range in quantities suilcient to assure that each of said remaining circuits will always require some attemperating liquid to hold the vapor temperature therein at said predetermined value.

3. The method of regulating vapor temperature in a fuelred forced ow once-through vapor generator wherein the entering liquid is vaporized and then passed in parallel flow relation to a plurality of parallel flow vapor superheating circuits, which comprises maintaining the temperatures of the vapor discharging from said superheater circuits at a substantially uniform and constant predetermined value over a wide range of loads by supplying attemperating liquid to one of said circuits in response to deviations of the vapor temperature therein from said predetermined temperature value in direction tending to increase the attemperating liquid supply rate as the vapor temperature increases and vice Versa, and by varying the tiring rate in response to deviations of the vapor temperature in the other of said circuits from said predetermined temperature value in direction tending to increase the tiring rate as the vapor temperature in said other circuit drops below said predetermined value and vice versa, while continuously supplying attemperating liquid to said other circuit throughout said predetermined load range in quantities suicient to assure that said one circuit will always require some attemperating liquid to hold the Vapor temperature therein at said predetermined temperature value.

References Cited in the le of this patent UNITED STATES PATENTS 2,752,899 Kasak July 3, 1956 2,840,054 Rowand June 24, 1958 FOREIGN PATENTS 787,006 Great Britain Nov. 27, 1957 

1. THE METHOD OF REGULATING VAPOR TEMPERATURE IN A FUEL-FIRED FORCED FLOW VAPOR GENERATOR WHEREIN THE ENTERING LIQUID IS VAPORIZED AND THEN PASSED IN PARALLEL FLOW RELATION TO A PLURALITY OF PARALLEL FLOW VAPOR SUPERHEATING CIRCUITS, WHICH COMPRISES MAINTAINING THE TEMPERATURES OF THE VAPOR DISCHARGING FROM SAID SUPERHEATER CIRCUITS AT A SUBSTANTIALLY UNIFORM AND CONSTANT PREDETERMINED VALUE OVER A WIDE RANGE OF LOADS BY SUPPLYING ATTEMPERATING LIQUID TO ONE OF SAID CIRCUITS IN RESPONSE TO AN INCREASE IN VAPOR TEMPERATURE THEREIN ABOVE SAID PREDETERMINED TEMPERATURE VALUE, AND BY VARYING THE FIRING RATE IN RESPONSE TO DEVIATIONS OF THE VAPOR TEMPERATURE IN ANOTHER OF SAID CIRCUITS FROM SAID PREDETERMINED TEMPERATURE VALUE IN DIRECTION TENDING TO INCREASE THE FIRING RATE AS THE VAPOR TEMPERATURE IN SAID OTHER CIRCUIT DROPS BELOW SAID PREDETERMINED VALUE AND VICE VERSA, WHILE CONTINUOUSLY SUPPLYING ATTEMPEWRATING LIQUID TO SAID OTHER CIRCUIT THROUGHOUT SAID PREDETERMINED LOAD RANGE IN QUANTITIES SUFFICIENT TO ASSURE THAT SAID ONE CIRCUIT WILL ALWAYS REQUIRE SOME ATTEMPERATING LIQUID TO HOLD THE VAPOR TEMPERATURE THEREIN AT SAID PREDETERMINED TEMPERATURE VALUE. 